A) Field of the Invention
The present invention relates to a light radiating device and a spatial optical communication device, and more particularly to a light radiating device for radiating light toward the space, and a spatial optical communication device using such a light radiating device.
B) Description of the Related Art
Super luminescent diodes (SLD) have been studied for applications to semiconductor optical amplifiers and optical fiber gyro power sources. Light output from SLD has low coherence. The operation of SLD relies upon suppression of laser oscillation. However, SL light is emitted via a waveguide having a optical gain so that it can be modulated at high speed. From this reason, SLD has drawn attention in terms of a high speed spatial optical communication element.
The light beam spot (near field pattern) of SLD is very small. Therefore, if super luminescent light (SL light) radiated from SLD is converged by a convex lens or the like, SL light concentrates upon a fine area. The power density of the area upon which SL light is converged becomes large. During spatial optical communication utilizing SL light, it is not preferable that a large power is concentrated upon an unexpected point in the space.
It is an object of the present invention to provide a light radiating device having a relatively large beam spot.
According to one aspect of the present invention, there is provided a light radiating device comprising: a light radiating element; a light diffusion sheet for receiving light fluxes radiated from the light radiating element at a first plane of the light diffusion sheet and scattering or diffracting the received light fluxes, and radiating the scattered or diffracted light from an opposite second plane; and a light distributing member for distributing the light radiated from the second plane of the light diffusion sheet in a direction.
According to another aspect of the present invention, there is provided a spatial optical communication device having the light radiating device and a light receiving element for receiving light distributed from the light distributing member of the light radiating device.
The light diffusion sheet can make large the light beam spot of a light radiating device. It is possible to prevent a large light power from concentrating upon an unexpected fine area.